1. Field of the Invention
The present invention relates to an x-ray diagnostics installation having an x-ray image intensifier video chain, an image memory and a differencing unit for subtracting stored video signals from current video signals, and in particular to such an installation having a control unit for controlling entry and readout of data from the image memory in accordance with selected occurrences in a dynamic body cycle of a patient under examination.
2. Description of the Prior Art
An x-ray diagnostics installation is described in German OS No. 31 24 583 correponding to U.S. Pat. No. 4,433,428 wherein a first image, which may be integrated, of a first heart phase is entered into a first image memory and a difference signal associated with a second heart phase is read into a second image memory. The second image memory is connected to a difference forming stage, which is also supplied with the current video signal as well as the stored video signal corresponding to the first heart phase. The current video signal and the first heart phase signal are subtracted, and the maximum expansion and maximum contraction of the heart, and thus the movement of the organ, can thereby be seen. A disadvantage of this installation, however, is that it cannot be employed in connection with another type of examination technique, known as the path-finder technique, described below.
In the so-called path-finder technique, a continuing fluoroscopic image showing a catheter is superimposed with the representation of the vessels generated from subtraction angiography. The examining physician or technician can thereby identify the course of the vessel paths when the catheter is introduced, without the use of a contrast agent, and make use of this information in correspondingly controlling the catheter. Transfer of the path-finder technique to cardiac angiography, however, is not possible in conventional installations because subtraction angiography generates a static vessel image which is superimposed on a radiograph which is dynamic, specifically with reference to the heart. Thus the contours of the moving heart coincide with the contour supplied by the subtraction image only at a single point in time.